HOP 0188

abstract of observational proposal

The scientific goal of this study is to determine the chromospheric response to nonthermal electrons, at multiple wavelengths simultaneously, during the initial stages of solar flares. The chromosphere is the primary radiating source during flares, with the majority of flare energy emerging in the form of optical/UV lines and continua. This radiation is believed to be driven by electrons (and possibly ions) accelerated during flares, and provides a crucial diagnostic for the energy deposition. The chromosphere is also the location of hard X-ray footpoint sources – the bremsstrahlung emission that is the diagnostic for the nonthermal electrons, and thus a major clue to the fundamental process of particle acceleration and flare energization. The chromosphere is also understood to be the source of the hot, dense plasma that causes the dramatic brightening in coronal flare loops through the process of chromospheric evaporation.

The radiative hydrodynamic model of Allred et al. (2005) provides one of the most comprehensive simulations of chromospheric heating by relativistic electrons to date. This model predicts a specific response of both line and continuum emission on sub-second timescales to varying parameters of injected electron beams. The ROSA instrument is now able to image the solar atmosphere on these intrinsic timescales. It is a common user instrument at the Dunn Solar Telescope (DST) in Sunspot, New Mexico and incorporates 6 cameras, each synchronised to 50 microseconds, with filters in Ca II K, H-alpha, 3500 and 4170 continua, G-band, as well as the Fe I line. From the data obtained by this HOP we aim to undertake a thorough investigation of the flaring chromosphere, including the origin of white light emission, by comparing co-ordinated observations from ROSA, IBIS, Hinode, RHESSI, SDO, and other GBOs, with theoretical predictions.

request to SOT

We request that SOT run a modified version of Case Study #4, to study the impulsive phase of flares: 109"x109" FOV in Ca II H, G-band, and red, green and blue continua at 60 second cadence. The H-alpha line is omitted from this version due to the degradation of the filter. The cadence is reduced to 60 seconds as ROSA itself will be looking at similar wavelengths at its own ultra-high cadence; this will free up more bandwidth for EIS. SOT data will be primarily used for co-alignment purposes, but this dataset should still provide sufficient science quality data in the event of unfavourable weather at the DST.
SOT = 150 Mbits / 20 minutes = 1800 Mbits for 4 hours.

request to EIS

The proposed EIS study (QUB_HI-CAD_FLARE_2S-EXP_104"x104") comprises 16 repeats of the QUB_HI-CAD_FLARE_V1 raster, totalling approximately 1 hour, and will compliment ROSA and IBIS observations by determining the dynamic response of the upper chromosphere. EIS will provide Doppler and nonthermal velocity maps at the flare footpoints at temperatures higher than what is achievable from the ground. The study comprises many emission lines formed over a broad range of temperatures (0.05-18 MK), including 4 pairs of density sensitive line ratios. It is based on the early CAM_ARTB_RHESSI_* studies which have been successful in diagnosing the chromospheric response during flares, over a broad range of temperatures simultaneously, while preserving the spatial information (Milligan & Dennis 2009, Del Zanna et al. 2011, Milligan 2011; submitted). This study is also a potential candidate for use in response to the EIS flare trigger.

EIS Study Acronym: QUB_HI-CAD_FLARE_2S-EXP_104"x104"
TARGET: Flare
EXPOSURE TIME: 2s
RASTER: Scanning
SLIT: 2"
STEP SIZE 2"
FOV: 104"x104"
DURATION: 3.5 mins
LINES: He II, O V, O VI, Mg VI, Mg VII, Fe VIII, Fe X, Fe XI, Fe XII (dens. sens. pair), Fe XIII (dens. sens. pair), Fe XIV (dens. sens. pair), Fe XV, Fe XVI, Fe XVII, Ca XV (dens. sens. pair), Fe XXIII, Fe XXIV
VOLUME: 18 Mbits: x16 repeats = 300 Mbits/hour = 1200 Mbits/4 hours)

other participating instruments

ROSA: Ca II K, H-alpha, 3500 & 4170 continua, Fe I magnetograms, G-band (0.03s cadence, 70"x70" FOV)
IBIS: Na D1 Dopplergrams, Ca IR triplet (2-20s cadence, 85"x85" FOV)
SDO/EVE: MEGS-A (6-37nm; incl. He 304A line), MEGS-B (37-105nm; incl. H + He continua), MEGS-P (Lyman-alpha) (10s/0.25s cadence, sun-as-a-star observations) (N.B. EVE have agreed to change their daily 3-hour MEGS-B and MEGS-P campaigns from 05:50-08:50 UT to 14:30-17:30 UT to coincide with the ROSA observing schedule).
SDO/AIA: AIA will be included in play, taking high-resolution images in each of its 8 filters at 12s cadence.
RHESSI: RHESSI will be included in play, taking full-disk HXR observations each orbit.
SOHO/CDS: We wish CDS to run the FLARE_AR observing sequence, which comprises the He I, O V, Mg X, Fe XVI and Fe XIX lines. (~11 minute raster cadence, 180"x180" FOV).
ISOON: H-alpha core (60s cadence, full Sun)

remarks

NOTES (13-feb-13)
1. The study was run last July and captured a mid-C flare (http://star.pst.qub.ac.uk/~rm/eis_qub_flare/20120718/eis_movie.html), although for some reason, EIS missed the crucial impulsive phase (see frames 16 and 17). This is precisely why continuous observations are required in the future. But even during the decay phase when the GOES flux was at the ~C2 level, there is a remarkable level detail to be seen, even at 2 second exposures! You can even see the infamous "knot" at the top of the high-temperature loops as seen in many other events (frames 18-26).

Another example: http://star.pst.qub.ac.uk/~rm/eis_qub_flare/20110712/eis_movie.html (see frame 8).

2. For the previous HOP 188 run, SOT operated as follows:

Pre-flare:
AR monitoring Case 2 modified
Ca II H-line every 1 minute
Na I D magnetograms (Stokes V/I) every 5 minutes
R/G/B Continuum every 5 minutes (instead of G-band)

Flare response:
Ca II H-line
R/G/B continuum
H-alpha Line Center
20s cadence for 15 minutes after XRT flare flag

3. The SDO/EVE team have agreed to operate the MEGS-B detector (which sees the Lyman-alpha line, Lyman and He I continua, as well as many chromospheric/TR lines) from 15:00-18:00 UT in response to a RHESSI/DST Flare alert. MEGS-B is not being routinely used for flares due to unforeseen degradation.  

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The scheduling of the proposed HOP is determined by the seeing conditions at Sunspot, NM at the time of the observing campaign (currently scheduled for one week in July 2011). Typically, seeing conditions are optimal during the first few hours after sunrise (~14:00-18:00 UT). We therefore request that Hinode continuously observe the chosen Target of Opportunity (ToO) as chosen by the Max Millennium Chief Observers (MM_CO) in their Message Of The Day (MOTD) during this period, whether on the disk or at the limb. If weather conditions at the telescope are unfavourable at the time of the observing run, we believe that the proposed Hinode dataset will have great scientific merit on its own, and in conjunction with other space-based instruments, and should still be run (subject to activity levels on the Sun, preferably C1-class flares or greater).